Subject: Re: [Xen-devel] [PATCH] xen/x86/pvh: Use HVM's flush_tlb_others op
To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>
References: <1449966355-10611-1-git-send-email-boris.ostrovsky@oracle.com>
 <20151214152713.GC23203@char.us.oracle.com>
CC: <3.14+@char.us.oracle.com>, <linux-kernel@vger.kernel.org>,
        <stable@vger.kernel.org>, <david.vrabel@citrix.com>,
        <jbeulich@suse.com>, <xen-devel@lists.xenproject.org>,
        <#@char.us.oracle.com>
From: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= <roger.pau@citrix.com>
Message-ID: <566EE1C4.4080204@citrix.com>
Date: Mon, 14 Dec 2015 16:35:32 +0100
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:38.0)
 Gecko/20100101 Thunderbird/38.4.0
MIME-Version: 1.0
In-Reply-To: <20151214152713.GC23203@char.us.oracle.com>
Content-Type: text/plain; charset="windows-1252"
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1509
Lines: 38

El 14/12/15 a les 16.27, Konrad Rzeszutek Wilk ha escrit:
> On Sat, Dec 12, 2015 at 07:25:55PM -0500, Boris Ostrovsky wrote:
>> Using MMUEXT_TLB_FLUSH_MULTI doesn't buy us much since the hypervisor
>> will likely perform same IPIs as would have the guest.
>>
> 
> But if the VCPU is asleep, doing it via the hypervisor will save us waking
> up the guest VCPU, sending an IPI - just to do an TLB flush
> of that CPU. Which is pointless as the CPU hadn't been running the
> guest in the first place.
> 
>>
>> More importantly, using MMUEXT_INVLPG_MULTI may not to invalidate the
>> guest's address on remote CPU (when, for example, VCPU from another
>> guest
>> is running there).
> 
> Right, so the hypervisor won't even send an IPI there.
> 
> But if you do it via the normal guest IPI mechanism (which are opaque
> to the hypervisor) you and up scheduling the guest VCPU to do
> send an hypervisor callback. And the callback will go the IPI routine
> which will do an TLB flush. Not necessary.
> 
> This is all in case of oversubscription of course. In the case where
> we are fine on vCPU resources it does not matter.
> 
> Perhaps if we have PV aware TLB flush it could do this differently?

Why don't HVM/PVH just uses the HVMOP_flush_tlbs hypercall?

Roger.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/